The present invention generally relates to plasma polymerization film forming methods and, more particularly, plasma polymerization film forming methods suitable for, for example, the formation of a plasma polymerization coating for silicone rubber and other polymeric substrates used as a covering for electrical leads of implantable medical devices.
Synthetic polymers, especially silicone rubbers, are used for many medical applications because they are substantially inert materials exhibiting good biocompatibility. Silicone rubbers and other polymeric materials suffer from high surface friction and surface tackiness, and have rather poor abrasion and wear resistance. These characteristics are problematic for many medical applications.
High surface friction and surface tackiness, and poor abrasion and wear resistance are characteristics which are problematic for many medical applications. For example, pacemaker leads having a silicone rubber insulating coating or covering do not easily slide past one another within the venous system dramatically limiting their use in dual pacing applications. Hemostasis valves generally require the addition of silicone oils to enable catheters to slide through the valve opening.
Many other medical devices such as penile implants suffer from poor lubricity when silicone tubes are inflated within silicone restraints. Poor contact surface lubricity causes sticking and/or hampered or unpredictable sliding performance which may occur at inopportune times, such as during insertion of catheters. Poor slip characteristics between the catheter and the slide site may result in abrasion or erosion of the silicone coating/covering leading to undesirable exposure of the lead conductor.
Prior attempts of providing desirable characteristics to silicones and other polymers resulted in undesirable characteristics. Some methods weaken the polymeric material leading to premature failure. Others introduce undesirable compounds into the blood stream. There remains a need for an improved surface modification or coating which provides the benefit of lubricity while maintaining abrasion and wear resistance.
The present methods provide a substantially amorphous, conformal, protective, abrasion-resistant, lubricious fluoropolymer coating via a gas plasma deposition method. The coating method, according to one embodiment, involves generating a gas plasma by introducing a mixture of a fluorinated gas monomer and a hydrocarbon gas into an energetic ion field, such as an ion beam or the field produced by a radio-frequency source. The fluorinated gas monomer is selected from the group consisting of CF.sub.4, C.sub.2 F.sub.4, C.sub.2 F.sub.6, CF.sub.3.sub.2CO, CH.sub.2 CF.sub.2 and mixtures of the foregoing. The hydrocarbon gas is selected from the group consisting of C.sub.2 H.sub.2, C.sub.2 H.sub.4, C.sub.2 H.sub.6, and H.sub.2 and mixtures of the foregoing.
The present methods are particularly well-suited to the manufacture of electrical leads with lubricious, abrasion-resistant biocompatible properties. Other applications of the method are within the scope of this disclosure.